There's something ethereal about lakeside hotels. It's the light, mainly - the alchemical way it strikes water to reveal moods that vanish as swiftly as they appear.

The spectacle is best viewed from hotels that sit on a lake. Picture the overblown romance of Udaipur's Lake Palace, the Titilaka hotel jutting dramatically into Peru's Lake Titicaca, and now, in Tasmania, the enchanting Pumphouse Point - a former Hydro-Electric Commission pile in the middle of Lake St Clair.

That's Lake St Clair as in Cradle Mountain-Lake St Clair National Park, an ancient landscape carved by glaciers, cloaked in dense rainforest and contained within the 1.5 million-hectare Tasmanian Wilderness World Heritage Area.

Its indigenous name is Leeawuleena, meaning "sleeping water", an apt title for Australia's deepest lake.

When the sun deigns to shine - rarely during our visit - the water sparkles like mercury. All around are brooding mountains with classical names (Olympus, Orthys), forests of candy-striped snow gum and stringybark, and alpine moorlands riddled with wombats and wallabies.

From the air, the 1940s pumphouse shimmers on Lake St Clair at the end of a 245-metre flume (a jetty atop an enclosed channel). Beneath a darkening sky in torrents of rain, former RAF pilot Jethro Nelson brings our De Havilland Beaver seaplane to a gentle splash on a platypus-friendly lagoon beside the lake.

Lodge manager Josh Bradshaw ferries us to land by motor boat for the short walk to the hotel. It's raining softly on my face, but weather doesn't really matter when the outlook is this dramatic.

The surreal sight of a faintly Georgian-slash-Grecian building floating on water amid the wildness is hard to put into words, until architect Peter Walker nails it. "It's a little Neoclassical temple out in the middle of the lake," he says. And he's right.

No matter how many times I look at it, from whatever angle, I never fail to be delighted that a public works architect in the 1930s let his whimsy run free to create something this lovely so far from civilisation.

It has taken developer Simon Currant, the man behind landmark Tasmanian properties such as Peppermint Bay, Cradle Mountain Lodge and Strahan Village, 18 years to realise his plans for this exceptional site. In that time he has had to scale back some of his grander plans, including a James Bond fantasy of golf buggies spiriting guests along the flume and then ascending into the building. The global financial crisis ended that dream so instead Currant's energy has been channelled into transforming the pumphouse and the old substation (on the shore and now called The Lakehouse), into a modern, comfortable 18-room hotel.

The result, he says, is a hotel that's "much more about the experience of this place and the environment rather than what the rooms are like, and the food". Though both the rooms and food are very good.

This is not some super-élite lodge for the wildly rich, but a reasonably priced escape in the heart of one of Australia's most primitive and pristine landscapes. The Pumphouse was a shell when construction began. Walker and his Cumulus Studio co-founder Todd Henderson preserved standout heritage features such as the bay window ringed with a narrow balcony to showcase moody views across Lake St Clair to mounts Hugel and Rufus.

Currant's brief to the architects was straightforward: "don't muck up the architecture". So the concrete structures have not been touched. Their distressed paint-jobs stand testament to decades of exposure.

Conditions improve markedly - but gradually - once visitors step inside the tall, heavy doors. "We liked this idea that guests would slowly be brought into a more refined space," Walker says.

"The public lounges still have exposed pipes and the walls are lined with untreated Tasmanian oak. Then, in the suites, it's the same oak, but it's more refined; it's been stained and smoothed."

There's a similar laissez-faire but generous attitude to breakfast and dinner. The former is a help-yourself affair of muesli, the kitchen's baked beans, and often eggs from Currant's spangled Hamburgs. "Absolutely free-range, happy eggs," he insists.

Dinners are prepared in Hobart then vacuum-sealed and sent to the wild north-west. They are likely to feature baked Scottsdale hams, heirloom carrots grown by Hmong migrants in the Derwent Valley and a warm orange polenta cake with vanilla bean ice-cream.

There are honesty bars in both buildings and, honestly, nothing beats gazing out that bay window at water, mountains and light with a glass of something comforting to hand.

Guests can explore their surroundings on bushwalks ranging from 30 minutes to the six-day Overland Track (which ends just across the lake at Cynthia Bay), or on mountain bike and fishing outings (Bradshaw is an accomplished fishing guide).

There's also much to be said for the joys of quiet contemplation - either by a cast-iron French fireplace, or from the soft-top comfort of a king bed with ringside views of the light show.

Nearby attractions include lunch at the Derwent Bridge Wilderness Hotel where the pie with peas, mash and gravy is just the tonic for a bracing day in the bush, or take a picnic and paddleboat to explore far shores. And definitely visit The Wall in the Wilderness, sculptor Greg Duncan's homage to the central highlands. He's a gifted artist who manages to tease out incredible detail from timber to represent aspects of local life and history, including the hydro.

Wildlife is another compelling drawcard. My tally was rather poor - a plump Bennett's wallaby, a pademelon, a brace of black swans, and welcome swallows fluffed up like long-tailed pom-poms on my windowsill at dawn. But it's possible also to see echidnas (perhaps at breakfast, waddling past the picture windows), as well as wombats and wedgetails, crescent honeyeaters and pygmy possums. In the summer months a park ranger from the Tasmanian Parks &amp; Wildlife Service will guide evening walks for guests.

Of course, this being a World Heritage area, there has been resistance to the development. "It's a heritage-listed property in a World Heritage-listed area. There was a fair bit of sensitivity about what we could and couldn't do," Walker says.

But, as Bradshaw contends, this has been effectively an industrial site for 70 years. A hotel with a strong eco-focus is an inspired use for an abandoned pumphouse and substation. It might even help arrest the region's tourism decline.

Annual arrivals to Lake St Clair have fallen from 102,000 people in 2002 to 70,000 last year, according to Tasmania Parks and Wildlife Service figures. With Pumphouse Point now open, I can't think of a better reason to visit.